Transmit-receive switch wherein branch line gas cell has resonant iris at its low power port, whereby iris is protected from peak power



22, 1967 s. o. SCHREYER 3.337.819

TRANSMIT-RECEIVER SWITCH WHEHEINBRANCH LINE GAS CELL HAS RESONANT IRIS AT .ITS LOW POWER PORT, WHEREBY IRIS IS PROTECTED FROM PEAK POWER Filed April 23, 1965 INVENTOR STAFFORD .0. SCHRfYf/P RECEIVER :ATTORNEY AGENT United States Patent M 3,337,819 TRANSMIT-RECEIVE SWITCH WHEREIN BRANCH LINE GAS CELL HAS RESONANT IRIS AT ITS LOW POWER PORT, WHEREBY IRIS IS PRO- TECTED FROM PEAK POWER Stafford D. Schreyer, Laurel, Md., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 23, 1965, Ser. No. 450,562 3 Claims. (Cl. 333-7) This invention relates generally to radio frequency transmitting receiving apparatus and more particularly to an improved transmit-receive switch that ensures adequate protection of the receiver when a single antenna is used for both transmitting and receiving radio frequency energy.

When it is desired to use a single antenna for both transmitting and receiving apparatus, there is a problem of ensuring that maximum use is made of available energy presented to the antenna and received from the antenna. The simplest and most effective solution is the use of a switch that physically transfers the antenna connection from the receiver to the transmitter during the period of transmission of energy. For most applications, especially when it is required to switch from transmit to receive mode in a few microseconds, available mechanical or electromechanical switches are inadequate, since none have a fast enough switching time. Therefore, it is necessary to use some electronic switch configuration in fast switching applications.

Numerous prior art switches and techniques for using these switches have been developed in transmitting-receiving apparatus and are known as T-R and AT-R switches. These devices normally have a gas-filled tubular member with electrodes and an ionizable gas. In some cases, it is necessary to have a resonant member and an ionizable gas or other conducting medium interposed between the source of radio frequency energy which is present in the main waveguide section to the antenna. The resonant member or iris usually is positioned in the receiver waveguide and may be constructed with a narrow slit in order to increase the value of the microwave field at the interface with the gas which reduces the breakdown of the gas. Once the gas breaks down or vaporizes, the resonant member will be essentially detuned from the transmitted frequency and the impedance seen at the slit by the waveguide is decreased to an approximate short circuit which effectively seals the opening to the receiver and passes the pulse energy to the antenna. When there is no transmission of radio frequency from the transmitter,

the resonant member provides a high impedance as the received signals are not strong enough to ionize the gas and the receiver is coupled to the waveguide to give a maximum transfer of energy.

As modern microwave apparatus has increased its level of radio frequency microwave operating power, the provision of a satisfactory T-R switching apparatus has become more troublesome, since with conditions of high incident average power, high loss in the gas discharge, or high duty factor or use of metals in the resonant member of poor thermal conductivity, adverse conditions may occur that result in the severe heating and possible destruction of the resonant member. Also, the normal glow discharge of the gaseous stage could change to an abnormal glow or arc in which high current densities could cause severe heating of the resonant member with a resulting increase in recovery time of the enclosed gas volume. Heavy discharges of this sort in the vicinity of the window or resonant member causes a condition known as sputtering. This condition exists due to a discharge across the Window or resonant member of sufficient intensity so 3,337,819 Patented Aug. 22, 1967 that metallic material is deposited upon the resonant member. Sufficient deposition results in detuning or short-circuiting of the resonant member resulting in poor receiver reception.

The instant disclosure provides an improved placement of the resonant member and gas capsule which will overcome the deficiencies present in the prior art. This apparatus provides placement of the gas capsule before the resonant member or resonant iris and immediately adjacent to the radio frequency energy. This results in both a reduction in recovery time of the gas and a temperature reduction of the resonant member, thus minimizing sputtering and eliminating the need of additional cooling means for the resonant member.

An object of the present invention is the provision of an apparatus that provides eflicient switching of microwave energy at high power levels.

Another object of the present invention is the provision of an apparatus that provides efficient switching of microwave energy at high power levels without destruction of the switching components.

A further object of the present invention is the provision of an apparatus that effectively protects the receiving system from high energy from the transmitting system.

Still another object of the present invention is the provision of a microwave switching apparatus that eliminates severe heating of the resonant member or iris of the apparatus.

Another object of the present invention is the provision of a microwave switching apparatus that eliminates sputtering at the iris of the resonant member in the system.

Still another object of the present invention is the provision of a microwave switching apparatus that has a shorter recovery time than prior microwave switching apparatus operating at the same relative power level.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing wherein:

The only figure in the case illustrates the improved microwave switching apparatus configuration in accordance with the present invention.

Referring now to the only figure in the case, there is shown a transmitter 11 and receiver 12 coupled by means of waveguide to a single antenna 13. Electromagnetic energy from transmitter 11 is conducted through a main waveguide member (not shown) to the antenna 13. Positioned at some point between the transmitter 11 and the antenna 13 is a section of waveguide 14 which couples the main waveguide to receiver 12. This section designated in the drawing as 14 is shown as a T section of waveguide. A metallic chamber is formed by the sides of the branch of the T and radio frequency window or iris 16. Positioned in this chamber is a glass box-shaped element 15 which is filled with an ionizing gas. Element 15 could also be constructed of any material which is transparent to microwave electromagnet energy. One side of box member 15 is adjacent to and flush with the inner wall of the T section 14. The radio frequency window or iris 16 may be formed with a slit 18. This window is usually formed of glass or other insulating material and is dimensioned so that it is resonant at the frequency of operation of the transmitting and receiving apparatus. The glass block 15 and radio frequency window 16 are fastened to the inner wall of the branch waveguide by cement or other suitable fastening means. Also positioned inside the branch of waveguide and immediately following the radio frequency window 16 is a member 17. This member is usually a gaseous tube of the TR type. A characteristic of this type tube is that it has a high resistance until the gas in the tube is ionized, and once ionized, the resistance is reduced to substantially a short circuit. Operation and structure of T-R tubes of this type are known to those skilled in this art and for that reason are not further illustrated or described. Immediately following member 17 and coupled to the T section by a section of Waveguide (not shown) is receiver 12.

In operation, energy from the transmitter during the transmitting cycle causes the gas in glass block member 15 to ionize, thus causing a glow discharge through its interior. This gaseous discharge absorbs some of the radio frequency energy before it reaches the radio frequency window member 16 and reduces the possibility of the condition of sputtering. The microwave element 16 which is resonant to the operating frequency of the transmitter will cause a high potential to exist from the energy remaining and this remaining energy will cause a glow discharge in the T-R tube, thus preventing or substantially reducing the amount of transmitter energy coupled to the receiver. Once the transmitting cycle is over, the receiver is immediately coupled to the antenna. The received energy, of course, is not high enough to break down the gas in the glass box 15 and the T-R tube, and, therefore, is coupled to the receiver through high impedance.

The present invention provides an effective, protective T-R switch for high power microwave apparatus. By use of the configuration disclosed, severe heating and possible destruction of the radio frequency window or iris is eliminated. Also, since heavy discharges of energy are not across the radio frequency window, the problem of sputtering is not present and window life will be increased.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A microwave switching assembly for providing etficient switching of high power radiant energy levels, comprising:

rnain waveguide means coupled between a source of radiant energy and a radiator of radiant energy; branch waveguide means coupled to said main wave- 4- guide means so as to have its longitudinal axis perpendicular to the longitudinal axis of said main wave guide, said intersection of said branch and main waveguide sections forming an opening in a first plane of substantially the same physical dimensions as the cross-section of said main Waveguide;

gas chamber means positioned adjacent said opening and being of substantially the same cross-section as said branch member; and

-a resonant iris positioned in said branch waveguide adjacent said gas chamber means and in a second plane parallel to said first plane,

whereby high power radiant energy from the source traveling in the main waveguide ionizes the gas in said gas chamber means to effectively reduce the energy discharge across the resonant iris thereby preventing sputtering.

2. A microwave switching apparatus for a transmitter receiver system having a signal antenna that provides protection of the receiver from high power transmitter energy, comprising:

a section of T waveguide, coupled between the transmitter and antenna;

gas chamber means positioned inside and adjacent the junction of said T section; and

resonant means positioned behind said gas chamber thereby providing a protective switching means for said receiver system.

3. The microwave apparatus of claim 2 wherein said resonant means, comprises a resonant Window.

References Cited UNITED STATES PATENTS 2,403,055 9/1946 Fiske 333 13 2,519,795 3/1950 Smullin 333 13 2,524,268 10/1950 McCarthy 333-13 2,734,171 2/1956 Heins 333 9s X 3,268,757 8/1966 Woermbke 333 13 X HERMAN KARL SAALBACH, Primary Examiner.

M. NUSSBAUM, Assistant Examiner. 

1. A MICROWAVE SWITCHING ASSEMBLY FOR PROVIDING EFFICIENT SWITCHING OF HIGH POWER RADIANT ENERGY LEVELS, COMPRISING: MAIN WAVEGUIDE MEANS COUPLED BETWEN A SOURCE OF RADIANT ENERGY AND A RADIATOR OF RADIANT ENERGY; BRANCH WAVEGUIDE MEANS COUPLED TO SAID MAIN WAVEGUIDE MEANS SO AS TO HAVE ITS LONGITUDINAL AXIS PERPENDICULAR TO THE LONGITUDINAL AXIS OF SAID MAIN WAVEGUIDE, SAID INTERSECTION OF SAID BRANCH AND MAIN WAVEGUIDE SECTIONS FORMING AN OPENING IN A FIRST PLANE OF SUBSTANTIALLY THE SAME PHYSICAL DIMENSIONS AS THE CROSS-SECTION OF SAID MAIN WAVEGUIDE; GAS CHAMBER MEANS POSITIONED ADJACENT SAID OPENING AND BEING OF SUBSTANTIALLY THE SAME CROSS-SECTION AS SAID BRANCH MEMBER; AND A RESONANT IRIS POSITIONED IN SAID BRANCH WAVEGUIDE ADJACENT SAID GAS CHAMBER MEANS AND IN A SECOND PLANE PARALLEL TO SAID FIRST PLANE, 